Overkill - what a stupid word. Sorry but true. Dead is dead period. Personally the 7 mag is probably the better set up and probably the most accurate of the 2 you have. Now don't get me wrong. I love the .270 Win. Just not in the Rem 710 (sorry).
IMO anything from a .243 Win on up is capable of cleanly taking a whitetail. So whatever fits you and works best for you, go with it. If you like the 710 better, I suggest you put the Leupold on that rifle and use it. Otherwise, use the 7 mag.